CDU Contributing Writer

As evidenced by numerous presentations at many of the spring 2002 medical conferences, there is a growing realization that time to defibrillation is the key to decreasing the incidence of sudden cardiac deaths in the U.S. In previous years, the number of sudden cardiac deaths has been cited as being between 300,000 and 400,000. The number quoted at the 2002 conferences was 250,000 – with the explanation that the change was due to either better statistical reporting or lowered incidence of overall heart disease. Still, the 250,000 represents 50% of all cardiac deaths and is reason enough for the emphasis on further reducing these deaths. The concentration on decreasing the deaths that occur out of hospitals is a reaction to the dismal 5% survival rate once someone on the street suffers a sudden cardiac event. Automatic external defibrillators (AEDs) have already demonstrated great potential to decrease time to defibrillation and therefore reduce the number of deaths – both in and out of hospitals.

Clinical studies have shown that 40% to 50% of all sudden cardiac arrests are due to either ventricular fibrillation (VF) or ventricular tachycardia (VT) – conditions in which the heart is "quivering" (VF) or beating so rapidly that the heart does not allow time for filling (VT). In either VF or VT, the patient quickly collapses, and death follows within minutes if there is no intervention. The other causes of sudden cardiac arrests are pulseless electrical activity and asystole, two conditions not corrected by using an AED. No matter what the cause, once an arrest occurs, every minute that passes without defibrillation decreases the victim's chance of survival by 7% to 10%. A delay of over 10 minutes diminishes the survival rate to nearly zero.

Studies conducted as early as 1987 have documented that sudden cardiac arrest victims treated by emergency medical technicians (EMTs) using standard defibrillators fared the same as those EMTs who used an AED. The rate of admission for victims treated with a manual defibrillator was 50%, while the AED group's rate was 54%. Survival to discharge for the manual group was 23% and only 30% for the AED victims. This and other studies demonstrated the reality that time to defibrillation, rather than the need for trained personnel as first responders, was an essential key to survival.

One study emphasizing this early defibrillation fact published the results of training security guards at a Las Vegas casino to use AEDs on suspected victims of cardiac arrest. The average time of collapse to AED defibrillation was 4.4 minutes with 58% of survivors eventually being discharged from the hospital. In a different study conducted from 1997 to 1999, AEDs were placed on American Airline (Fort Worth, Texas) flights. Of the 14 cases of documented ventricular fibrillation, 40% of the people survived to discharge without neurological impairment.

From these and other studies, it became apparent that AEDs in the hands of lay people were becoming an important adjunct in the efforts to improve the chances of survival for people suffering out-of-hospital sudden cardiac arrest. The American Heart Association (AHA; Dallas, Texas) now states that it strongly advocates that all EMS first-response vehicles and ambulances be equipped with an AED or another defibrillation device (semiautomatic or manual defibrillator). The AHA also supports placing AEDs in targeted public areas such as sports arenas, convention centers, theaters, churches, office complexes, doctors offices, shopping malls, etc.

There are two main areas in which the use of AEDs is important and in which usage is increasing. Hospitals are an obvious site, especially because of the depressing 15% in-hospital survival to discharge rate for cardiac arrest victims. That dismal 15% figure has remained constant in spite of basic life support teams, advanced life support teams and improved manual defibrillators. However, public-access use of AEDs is the prime AED market because the majority of the sudden cardiac arrests occur outside of the hospital. Indeed, research is showing that three-fourths of all cardiac arrests occur in the home – a statistic that has not escaped the attention of vendors in the defibrillator/AED market niche.

The four major vendors in the AED market include Philips Medical (Andover, Massachusetts), Medtronic/PhysioControl (Redmond, Washington), Cardiac Science (Irvine, California) and Zoll Medical (Burlington, Massachusetts). Two newcomers are MRL (Wheeling, Illinois) and Access CardioSystems (Concord, Massachusetts). Access CardioSystems was started in 2000 by an emergency physician and a medical device businessman. MRL is not new to defibrillators, but is a new manufacturer of units with biphasic waveforms. Older manual defibrillators used monophasic waveforms – with energy flowing in only one direction and therefore requiring higher energy levels to successfully disrupt VT or the more chaotic VF. But there often were side effects, including damage to the left side of the victim's heart and possible external chest burns. All major competitors in the AED market now utilize biphasic waveforms that deliver a charge in one direction for half of the defibrillation sequence and then a charge in the electrically opposite direction for the second half – with a dramatic lessening in side effects. The survival rates for early defibrillation and the decrease of the side effects with biphasic waveforms have generally been impressive.

Each of the major AED competitors is seeking to determine which of the biphasic variation nuances is most effective and have the fewest side effects when used, as well as how to circumvent the intellectual properties of their rivals. This situation is not unlike two earlier periods involving damped sinusoidal and trapezoidal waveform research and utilization. While the current climate continues to find disagreement on the distinctions of the various waveforms, there are significant differences in biphasic waveforms and energy levels.

The four major suppliers of biphasic AEDs (Philips, Zoll, Medtronic/PhysioControl and Cardiac Science) segment into two different biphasic camps – a lower energy camp (Philips and Zoll) and a higher energy camp (Medtronic and Cardiac Science). As might be expected, these two differing approaches compete with each other.

The low energy vendors (those using energies of 120 joules to 170 joules or less) with impedance compensated biphasic waveforms suggest that the lowest effective level of energy is the best choice for defibrillation with fewer side effects. The higher energy group (those devices using energy levels in excess of 170 joules) argues that the efficacy is improved if the defibrillator has an energy reserve that can be tapped if low energy shocks are not effective in converting the patient to an adequate rhythm. The lower energy vendors counter this argument by pointing out that many factors (including elapsed time to shock and others) affect the success of conversion as much or more than the energy level and must be controlled or eliminated to truly evaluate energy level effectiveness, which has not yet been accomplished or studied.

To assist in determining which of these two differing arguments is correct, the AHA has published guidelines (see Table 3 on page 6) that include several classes for defibrillators to be categorized in, depending upon their demonstrated effectiveness (based upon proven available scientific evidence). The most effective units are qualified as AHA Class 2A devices. The AHA has classified other units that have not proven to be as effective as Class 3 devices. However, devices in the low-energy camp (Philips and Zoll) are all AHA Class 2A devices, while one of the higher-energy AED devices from Cardiac Science is a Class 3, according to the company.

Each of the vendors finds its AED device in one of the above categories. Philips' waveform and autoimpedance sensing initially achieved a Class 2B designation but, upon further research, has been qualified to Class 2A. Zoll's AED, with its rectilinear biphasic waveform and autoimpedance adjustment, also is classified as Class 2A, even though the waveform is slightly different than the Philips Heartstream Smart Biphasic (truncated exponential biphasic) waveform. The Heartstream device has been used successfully to convert patients weighing up to 700 pounds, with a measured impedance of around 170 Ohms. The higher-energy AED from Cardiac Science is classified into Class 3 at present.

Nevertheless, success in the AED market and improvement in survival rates will depend more on other factors than which waveform a particular device employs. The waveform divergence is more likely to be important in the hospital segment than in the public segment. In the public sector, the cost of the device may be more significant than the waveform or any other factor, as long as it is a Class 2A or 2B device and it is easy and intuitive to use. The low-cost leader is Access CardioSystems, with its $995 AccessAED device, followed closely by Zoll with its AEDPlus, which costs around $1,600. Competitive units range in price from $3,000 to $3,500 or more. Zoll's AEDPlus is not only intuitive, but has voice activation once the unit is turned on that talks the responder through the steps of rescue – from "Call 911" to placement of the electrodes and the need to stay clear while the unit deploys.

Competition among vendors with new products often results in larger companies having an advantage over smaller companies, no matter how good or bad their technology may be. However, one aspect that levels the playing field is the simple fact that the vast majority of the units sold will be purchased by various first responders and for public access areas, and therefore hospital group purchasing organizations will not be able to dictate the major thrust in the AED market. Nonetheless, access is a formidable issue to companies such as Zoll and MRL compared to Medtronic/PhysioControl or Philips.

The size of this market is enormous, as large office buildings, stadiums and arenas, concert halls, airports and other public buildings are candidates for multiple units, as is every police car, train and bus. Finally, at $995 each, every Class 3 or Class 4 congestive heart failure patient is a potential customer. Taken together, this is a medical technology sector to watch and in fact may be large enough for all players to multiply their defibrillator revenues by factors of five or 10 times.